1. First of the Invention
The present invention relates in general to power steering devices for wheeled motor vehicles, and more particularly to power steering devices of a so-called multiplex type. More specifically, the present invention is concerned with the power steering devices of the multiplex type which includes a main steering drive system which drives a steering mechanism of the power steering device and a sub-steering drive system which drives the steering mechanism when the main steering drive system fails to operate.
2. Description of the Related Art
One of the power steering devices of the above-mentioned multiplex type is shown in Japanese Laid-open Patent Application (Tokkai) 2002-037112. The power steering device of this publication has a steering drive mechanism which comprises a main steering drive system and a sub-steering drive system. An actuator of the main steering drive system and an actuator of the sub-steering drive system are mechanically linked to each other through a link mechanism with a play and these two actuators are constantly driven under operation of an associated vehicle engine. A mutual interference detecting mechanism is provided for detecting presence/absence of interference between the main steering drive system and the sub-steering drive system. When it is found that there is some abnormality in the main steering or sub-steering drive system, a control section of the main steering or sub-steering drive system shuts down its steering drive system. While, when, under normal condition of the main steering or sub-steering drive system, it is found that a mutual interference is detected, the control section of the main steering or sub-steering drive system forcedly stops operation of the counterpart drive system, viz., the sub-steering or main steering drive system. With this, output depression of the steering driving system can be minimized and thus an assured fail-safe operation is obtained.